Need help to recreate this shape in blender
Use Boolean modifier to do such Hollows in Mesh:

See how it woks:

You can do these on Default cube when Blender is Opened with Default Settings.
Just add two modifiers:
1. Bevel:


Add Subdivision Surface(Subsurf) Modifier..
And change the view and render both to 3.

Scale it according to your object by pressing S. If you want to scale your object particularly on one axis (after pressing S)pressX/Y/Z respectively.

Now Duplicate your object by Shift+D and pressY to move it only on Y axis.

Now scale the Duplicated cube down to Z axis, it depends on how much you wish the hollow size to be.Make sure you scale more on X axis to make whole visible from outside of the actual cube.

Now take the duplicated cube and move it inside the Actual cube by moving it on Y axis.(PressGandY)



  Now this is important.


Select the Actual cube and add Boolean modifier to it.

Go to Boolean Modifier Settings and select the duplicated cube. There's only one so it will show it only one. Select it.

Edit:
Click on the drop down in side of the selection:
Change it from Intersect to Difference.

Now apply the Boolean modifier of the Actual cube.

Now you can delete the duplicated cube you will see the Hollow in the cube.

You are done.


  If Bevel and Subsurface Modifiers don't work well for your mesh, you
  can just go to Edit Mode, Press A if your mesh is  not selected and
  Press Shift+Ctrl+B and scroll Mouse
  wheel to make changes, you will notice some changes in corners of your
  Cube, Plane,etc. It works same as the combination of Bevel and Subsurface Modifiers


Check out this Boolean.blend file.
Check Modifiers Stack.


  It is not necessary to duplicate and hollow, you can add any object
  like UV Sphere and do the same. But now UV sphere will act as
  Duplicated cube.  Imp: Add Boolean Modifier only to the object you
  want to hollow. Not which you are using to Hollow.


Happy Modelling!